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采用原子态分辨(Atomic-state-dependent, ASD)屏蔽模型，研究了热稠密等离子体中Fe25+离子光电离截面的低能特征。等离子体屏蔽会减弱核和束缚电子之间的相互作用，导致束缚电子逐渐进入连续态。对于光电离过程，屏蔽效应改变束缚和连续电子的波函数，进一步改变重叠积分和跃迁矩阵元，最终引起截面出现低能特征。相比于传统的德拜模型，ASD模型进一步考虑了电子简并效应和非弹性碰撞过程的影响，能够更加准确的描述温热稠密等离子体的屏蔽效应。基于ASD模型，研究发现，低能阈值区，截面服从Wigner阈值定律；能量逐渐增大时截面出现低能增强、势形共振、Cooper极小、Combet-Farnoux极小等低能特征，导致对应能区的截面显著增加或减小，继而改变光电子谱的性质。本工作研究了热稠密等离子体中离子的光电离过程，可以为天体和实验室中热稠密等离子体的研究提供理论和数据支持。Complex multi-body interactions between ions and surrounding charged particles exist in hot and dense plasmas. It will screen the Coulomb potential between the nucleus and electrons, and significantly change the atomic structures and dynamic properties. This will further affect macroscopic plasma properties such as radiation opacity and the equation of state. Based on the atomic-state-dependent (ASD) screening model, we investigate the photoionization dynamic of Fe25+ ion in hot and dense plasmas. The photoionization cross section for all transition channels and total cross sections of n ≤ 2 states for Fe25+ are studied in detail, as well as the low-energy characteristics induced by plasma screening. Compared to the classical Debye Hückel model, the ASD model incorporated the degeneracy effects by inelastic collision processes, resulting in higher plasma density requirements for bound electrons to merge into the continuum. Near the threshold, the photoionization cross section obeys the Wigner threshold law after considering the screening effect. As the energy increases, the cross sections show low-energy characteristics such as shape resonance, Cooper minimum, low-energy enhancement, and Combet-Farnoux minimum, etc., which can significantly increase or decrease the cross section of the corresponding energy region. For example, the low-energy enhancement in the 2p→εs1/2 channel increases the cross section by several orders of magnitude, drastically changing the properties of the photoelectron spectrum. It is significant to study the low-energy characteristics for understanding the physical properties of the photoionization cross section. Fe is an important element in astrophysics. The cross section results in the middle and high energy region calculated by the ASD model in this paper can provide theoretical and data support for the investigation of hot and dense plasmas in Astrophysics and laboratory situations.
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